1. Field of the Invention
The present invention relates to processes for the preparation of silicate charges containing plastic compositions, a polymeric composition containing silicate charges in particular, master batches, by co-precipitation techniques. The present invention also relates to the silicate containing plastic compositions resultant from the co-precipitation process.
2. Description of the Prior Art
The art of reinforcing elastomeric materials has actively pursued methods and materials for effectively incorporating white fillers or charges within an elastomeric composition. Primary emphasis has been laid on the incorporation of silica as such a charge or filler material. Conventionally, the charge is added to or formed within a mixture which is to be vulcanized subsequent to the incorporating of the charge therein. While this facilitates control of the formation of the set charge, unfortunately control of the incorporation of the charge into the resulting vulcanized elastomer is quite difficult.
It has also been proposed to use mixtures of a charge and an elastomer; however, heretofore this approach has resulted only in the coating of the silica agglomerates, but not in formation of aggregates. "Co-precipitation" of silica or silicates and a rubber latex have been examined in an effort to provide a useful product. Yet major difficulties are encountered in arriving at a homogeneous precipitation of the latex and the filler charge. This is due to the fact that the reference to "co-precipitation" is, technically, a misnomer. In effect, if the reaction is effected by simply adding an acid to the mixture of the latex and a soluble silicate, silica will precipitate gradually over the pH range of from about 3 to about 10, while the latex emulsion does not break down until a pH on the order of 5 is achieved. Therefore, there is not, in actuality, a simultaneous precipitation of silica accompanied by coagulation of latex. However, because the art speaks in terms of "co-precipitation", the present specification will do so likewise.
The impetus for activity in the investigation of co-precipitation of silica or silicates and rubber latex regards the desire to obtain homogenous precipitation, whereby silica- or silicate-containing master batches may be prepared for ease of incorporation of the charge within an elastomeric material. To date, however, none of the prior art processes directed to this end have resulted in the ability to obtain a good dispersion of the charge within the elastomer.
It has been proposed, in U.S. Pat. No. 2,485,287, to admix a dilute coagulable aqueous dispersion of polymeric materials with a dilute aqueous solution of a water-soluble chemical reagent which has substantially no coagulating action on the dispersion, and introducing an aqueous solution of a second water-soluble chemical reagent which is reactive with the first in the formation of insoluble materials and which also is capable of coagulating the dispersion. According to this patented procedure, the coagulating reagent must be supplied in excess amounts over that necessary to bring about reaction with the first reagent if coagulation is to proceed. It is obvious that the procedure, in accordance with this method, is complicated, and requires a great many precautions to yield a serviceable product. Additionally, the present inventors have determined that processes such as this have many critical parameters, particularly pH, which must be followed closely if the process is to work at all.
The art also recognizes, as a general matter, various processes for precipitating or coagulating dispersions of rubber or similar types of material. Along these lines, note U.S. Pat. No. 1,970,469 which discloses the double decomposition of one or more water-soluble reagents having normally no coagulating effects upon rubber-containing dispersions with one or more water-soluble reagents capable of reacting with the first to produce insoluble compounding ingredients. Carbonates, sulfates, silicates of the alkali metals or of ammonium are noted as examples of the first water-soluble reagents; while, soluble salts of magnesium, aluminum, calcium, barium, or zinc are noted as useful for the second enumerated water-soluble reagents.
Accordingly, the need exists to provide an improved filler or charge material, based upon silica-latex mixtures, for incorporation in elastomeric materials. The need also exists to provide an improved, simplified, and more efficient process for the production of these products.